Large distributed switching systems for telecommunication services traditionally include an administration module and a centralized processor. The centralized processor may be located within the administration module, or located outside of the administration module, but closely coupled thereto. The centralized processor controls switching functions in response to inputs from its nodes according to a program stored in the centralized processor's memory. These nodes may include switching processors or other processors. The centralized processor controls and supervises a number of the switching modules which contain the switching processors. The switching modules are where the large distributed switching system connects to external voice and/or data units by various lines and trunks. The switching processors of the switching modules have traditionally controlled the real-time intensive tasks, such as signal processing and time slot interchanging, in response to stored programs in their memories. One example of such a system is shown in U.S. Pat. No. 4,382,294 entitled "Telephone Switching Control Arrangement," by Beuscher, et al. This patent is commonly assigned to the assignee of the present invention, and is hereby incorporated by reference.
In a known large distributed switching system, the overall control of hunting a trunk to complete a call is provided by the centralized processor. The centralized processor has centralized information regarding the availability of each trunk that terminates at the switching system: information that the distributed switching processors do not have. After the centralized processor receives a trunk request to complete a call via one of the switching processors, the centralized processor searches a bitmap representing the availability of the group of trunks that are connected to the distributed switching system at one end and another switching system or a base station system for wireless communications that is the object of the trunk request at the other end. Each bit position in the bitmap represents a specific trunk of the trunk group that terminates at the switching system. If a trunk is unavailable, i.e. busy, its corresponding bit position in its bitmap will be a binary 0 and if it is available, i.e. not busy, its corresponding bit position will be binary 1. The centralized processor then searches through the relevant bitmap using any of various search algorithms until it finds an available trunk to fulfill the request. Data associated with each trunk respectively identifies the switching module at which each trunk terminates. When an available trunk is selected, the centralized processor sends instructions to the switching module, which terminates the selected trunk. The instructions instruct the switching processor of the switching module to set up the requested connection.
A problem has arisen in switching systems having multiple switching modules as the switching modules have grown in their capacities. Because of this growth, the switching modules and their switching processors in aggregate are capable of handling more call processing tasks than the centralized processor is capable of controlling. Furthermore, the long term tendency for the switching processors, which are commercially available microprocessors, is even further growth in processing capacity. Thus, the mismatch of capacities between the centralized processor and the switching processors will tend to grow even worse. This problem is heightened in distributed switching systems that have many switching processors because a centralized processor with multiple switching processors must grow its capacity accordingly just to keep pace and not become the limiting factor of the distributed switching system. Thus, there is a need within the art to allow switching module and switching processor capacities to grow without outgrowing the capacity of the centralized processor to control and supervise the switching system functions.
It is an object of the invention to reduce the need to grow the capacity of a centralized processor in a telecommunication switching system.
It is an object of the present invention to provide a method of hunting certain trunks by the switching processor of a switching module thereby reducing the control and supervision load of the centralized processor in a distributed system.
It is another object of the invention to provide a switching system that uses the switching processor of a switching module to hunt some trunks without involving the centralized processor.
It is another object of the invention to provide a commonly accessible record of trunk availability that is updated on a real time basis.